Alexander muirhead



(No Model.)

A. MU'IRHEAD.

Duplex and Multiplex Telegraph.

No. 230,802. Patented Aug. 3,1880.

W I T JV ESSES I NVENTOJP ,By his .dttorneys,

UNITED STATES PATENT ALEXANDER MUIRHEAD, OF OAKWOOD, FARQUHAR ROAD, UPPER NORWOOD, LONDON, ENGLAND.

DUPLEX AND MULTIPLEX TELEGRAPH.

SPECIFICATION forming part of Letters Patent No. 230,802, dated August 3, 1880.

Application filed March 24, 1850.

To all whom it may concern:

Be it known that I, ALEXANDER MUIRHEAD, a subject of the Queen of Great Britain, doing business at 29 Regency Street, Westminster, England, and resident at Oakwood, Farquhar Road, Upper Norwood, London, England, have invented certain new and useful Improvements in Duplex and Multiplex Telegraphs, of which the following is a specification.

The object of my invention is an improvement in the mode or manner of regulating or adjusting the artificial lines or compensatingcircuits in systems of duplex and multiplex telegraphy, especially those used on aerial and underground lines.

It consists in introducing in the artificial line a leakage-circuit of a fixed resistance and varying its position with regard to the resistance of the artificial line.

In all successful systems of multiplex telegraphy in which a differential arrangement of the transmitting and the receiving apparatus is employed there is required for the accurate working of the system a circuit having exactly the same electrical resistance and capacity of the real line. Such circuits are called artificial lines or compensating-circuits.

Hitherto, in order to compensate further for the variations of insulation of the real line, it has been the practice to produce a similar effect in the artificial-line circuit by varying both its resistance and capacity, two operations which cause great delay in the working of the system. In my invention I compensate more quickly for these variations of insulations of the real line by simply inserting a leakage-circuit in the artificial line and varying its position until the resultant insulation resistance of the artificial line is the same as the insulation-resistance of the real line.

The leakage-circuit is of a resistance determined by trials for all to gix e the best results. From experience I find five thousand units re sistance a very convenient amount to have in this leakage-circuit.

In the drawings, which represent one mode of carrying out my invention, Figure 1 is a (No model.)

plan view of a rheostat and adjustable leakage-circuit, and Fig 2 a section through the line 2 2 of Fig. 1.

Rh is a rheostat, consisting of a series of coils 0r resistances, r r 1*, &c., to 2' These I prefer to make of Muirheads inductive re sistance, as described in United States Letters Patent No. 208,665, of October 1, 1878, to John Muirhead, Jr., for improx'ement in condensing-resistance, for electric telegraphs.

X is the adjustable arm of the rheostat, pivoted on the axis 00, with which it is in electric communication. Y is another arm work in g independently on the axis 00, but insulated therefrom, and also from the arm X.

3 is the leakage-circuit, made in this instance of ordinary German-silver or platinumsilver wire, one end of which is attached to the movable arm Y, and the other to earth.

a a are contact-points in the resistancecoils r 1- 1 &c., making contact, respectively, with the arm X of the rheostat and the arm Y of the leakage-circuit. The arm X is shown bent and making contact with the outer contactpoint a, so as to be completely insulated at all points from the leakage-circuit and its arm Y.

All variations in the insulation of the real line can be compensated for by simply varying the point of application of the leakagecircuit y-that is to say, supposing the resistance of the rheostat to be 9", corresponding to the resistance of the real line, all variations in the insulation can be compensated for by applying the leakage-circuit at any point from T to T In the drawings the leakagecircuit is represented as at W.

That I claim as new, and desire to secure by Letters Patent, is

1. The hereinbefore-described method of adjusting artificial lines or compensating-circuits in systems of duplex and multiplex tclegraphy, which consists in inserting an adjustable leakage-circuit in the artificial line and varying its position, substantially as and for the purpose described.

2. The combination of the artificial line and the adjustable leakagecircuit, substantially as described.

3. The combination of the leakagecircuit,

consisting of the insulated and adjustable arm In testimony whereof I have hereunto sub and .its resistance, with a rheostat consisting scribed my name this 27th day of February,

of a series of resistances and an adjustable 1880. rheostat-arni turning on the same axis as the leakage-circuit, but insulated therefrom, sub- ALEXANDER MUIRHEADu stantially as described.

4. The leakage-circuit consisting of the C0ll1- Witnesses:

bination of the insulated and adjustable arm andits resistance, the Whole operating substantially as described.

OHAs. EDGAR MILLs, WILLIAM D. WARD. 

